I received this in exchange for an honest review. I was hesitant to use this on my very barky Yorshire Yerrier. I was nervous that he was going to be in pain. But I did try it out on the lowest setting so that he would just get a little buzz when he went nuts at the mail carrier, the UPS guy and the Fed-Ex guy (which are our biggest problems). So he felt a little bit off when it happened. Not hurt though, but you could tell he didn't like it.
I only left it on during the those times when I knew those guys worked. I did not want my dog to stop barking at other times because I like to be alerted to when we know people are home or when there are people in the area around our house. Cocoa is good about that. This definitely worked for helping him to realize when it was okay to bark and when it was not. It took at least a week got him to really get the hint.